The present invention relates to a seat belt tensioning device for use in vehicles such as automobiles, more specifically to a seat belt tensioning device of the type that a piston which is connected to a seat belt is inserted within a cylinder.
The seat belt tensioning device of this type is provided with a piston operating means which moves the piston at an urgent time such as upon a vehicle impact.
According to this seat belt tensioning device, the seat belt is tensioned due to the movement of the piston. And as the piston operating means, gas pressure or the like is used.
However, it is very difficult to correctly adjust the seat belt tension force into a desired value by means of the piston operating means such as gas pressure.
Furthermore, in one example of the seat belt tensioning device of this type, the seat belt is connected to the piston through a deformable member which is plastically deformed and elongated due to a predetermined load and is drawn out of the cylinder.
However, according to such an energy absorbing means as described above, the deformable member is apt to be plastically elongated during the seat belt tensioning process.
And there is a problem that the drawn stroke is not sufficiently obtained after the piston is stopped.
Accordingly, one object of the present invention is to provide a seat belt tensioning device by which the tensioning force can be correctly adjusted to a desired value.
Still another object of the present invention is to provide a seat belt tensioning device which absorbs the kinetic energy of the occupants with certainty during a vehicle emergency.
Further object of the present invention is to provide a seat belt tensioning device having a simple construction.